The present patent application has for an object new, aryl-substituted 4,5-diaminopyrazoles and colorants for keratin fibers containing these compounds.
In the area of keratin fiber dyeing, particularly hair dyeing, oxidation dyes have attained substantial importance. In this case, the coloration is produced by reaction of certain developers with certain couplers in the presence of an appropriate oxidant. Now as before, hair colorants for dyeing in the natural color shade range are particularly important. In addition, by combination of suitable oxidation dye precursors, it is also possible to produce currently fashionable color shades. Currently popular are modified natural shades, for example brown shades with pronounced eggplant or copper tones and particularly brilliant red tones.
In addition to being able to produce color effects, oxidation dyes intended for use in treating human hair must meet many other requirements. Such dyes must be unobjectionable from a toxicological and dermatological standpoint, and the colorations achieved must show good light fastness, resistance to permanent waving, rubbing fastness, resistance to shampooing and sufficient resistance to perspiration. Moreover, by combination of suitable developers and couplers it must be possible to produce a wide range of different color shades.
In the past, the red range, which as before is important, was provided predominantly by use of 4-aminophenol as the developer. Because of concerns about the physiological compatibility of this substance, derivatives of pyridine and pyrimidine have also been used, but they were unsatisfactory from a coloring standpoint. A significant improvement in color stability in the red range was achieved for the first time by replacing p-aminophenol with 4,5-diaminopyrazoles described in EP-A 0 375 977. Moreover, DE-A 101 09 806 discloses combinations of substituted pyrazolones and 4,5-diaminopyrazoles to create yellow to orange shades.
Whereas most oxidation dyes hardly show any weaknesses on undamaged hair, major differences can arise on damaged hair. Hence, the hairdresser knows from his everyday practice the problem that dyes are not absorbed uniformly by the hair to be dyed. Whereas the hair roots are usually intact, the hair tips in the course of time show damage caused by the effect of weather factors and frequent washing and combing and which increases from the roots to the tips of the hair. When such hair is dyed, then because of the nonuniform hair structure between roots and tips, the coloring results can be nonuniform. Another problem lies in that during washing the dyes are more strongly washed out from the damaged hair regions than from the undamaged ones, which after a few hair washings can become gradually more noticeable depending on the degree of hair damage. In particular, the customer also notices this because the hair tips look dull.